Tunable resonator



June 4, 1946. N. E. LINDENBLAD 2,401,489

TUNABLE RESONATOR Filed Nov. 29, 1941 26 INSULA770N- lllllllllllllll FILAMENT CIRCUIT r0 F/MMF/W' HEAT/N6 q 20 c/ncu/r V I 7F 25 g. In '/7 I 24 m/smnrmmg 26 27 INVENTOR NILS E u DENBLAD wul/l/ ATTORNEY Patented June 4, 1946 2,401,489 TUNABLE RESONATOR Nils E. Lin'denblad, Port Jefl'erson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application November 29, 1941, Serial No. 420,936

12 Claims. 1

This invention relates to electrical resonator circuits for use at ultra high frequencies and particularly to a method of and means for tuning such resonators.

One of the objects of the present invention is to provide a cavity resonator at ultra high frequencies having improved tuning means for controlling the frequency of the resonator. A more specific object is to provide an ultra high frequency cavity resonator having a wider tuning frequency range than known cavity resonator circuits, and wherein tuning is efiiciently achieved by an arrangement which avoids the use of a sliding contact.

Other objects will appear from a reading of the following description which is accompanied by a drawing wherein Figs. 1 and 2 illustrate two different embodiments of the invention.

Fig. 1 illustrates an ultra high frequencycavity resonator comprising an upper wall H], a lower wall and-a side or end wall |2. The walls l and H may be in the form of circular metallic plates, While the end wall |2 may be in the form of a metallic cylinder joining walls I0 and II together at their peripheries. Obviously, the resonator may have other forms, such as a hollow rectangular prism. Located in the interior of the resonator l2 there are shown a plurality of vacuum tubes |3, |3, preferably of the acorn" type. which are adapted by reason of their short, well-spaced leads and other characteristics to operate on wavelengths of the order of onemeter and less. The grid of each of the tubes I3 is connected by meansoi a short metallic rod M to a plate 45 located on wall l0 externally of the resonator but capacitively coupled to the wall ID by means of insulation l6. Similarly, the anodes of the vacuum tubes l3 are each connected by means of short metallic rods |5 to a metallic plate I! mounted on the wall or plate externally of the resonator and capacitively coupled to the plate H by means of insulation IS. The grids and anodes are thus by-passed to the outside of the resonator by mean of capacitive paths of very low impedance to energy of the operating frequency. The filament legs of each vacuum tube are connected by means of plates l8 and I9, respectively, to filament heating leads 20 extending to a suitable source oiv heating current. Plates l8 and I9 are mounted on a central plate 2|. which is connected to the cathode of the vacuum tube, and by-passed to the plate 2| for energy of the operating frequency. It will be noted that the plates l8 and H! are insulated from plate 2| by suitable insulating spacers, preferably mica,

2 and that the plate 2| is connected to the side or end wall l2. Plates 45, H, l8, l9 and 2| may, if desired, be circular strips which are .centrally apertured, by means of which a. polarizing potential applied to any one of these plates will energize or polarize all of the corresponding electrodes of the various vacuum tubes connected to the same plate. The ring 2| constitutes in effect a rin shaped shelf which is grounded to the side or end wall l2 of the resonator, and to which the grid may be conductively connected through a grid resistor 23 to provide a suitable bias for the grid.

If desired, of course, each electrode of the vacuum tube may be connected to a separate metallic segment so that the current in each electrode of a vacuum tube can be measured separately in order to determine whether a vacuum tube is good or bad. For mounting the vacuum tubes in their desired position within the resonator, there may be provided an insulating ring 22 which has a wide central aperture. This insulating ring may preferably extend to the end wall l2 in order to be supported thereby. A battery 24 is shown having its positive terminal connected to the anode ring plate I! for providing a suitable positive polarizing potential on the anodes of the vacuum tubes. It should be understood that the two vacuum tubes l3, l3 shown are merely illustrative of a multiplicity of vacuum tubes symmetrically located within the resonator around the electrical center.

For tuning the resonator, there are provided a pair of hollow metallic elements 25, 25 which are positioned in the center of the resonator on opposite sides thereof where the voltage is a maximum. Each of the elements 25, 25 is mounted on an insulating support 26 which is movable in position to vary the spacing between the elements 25, 25. Each tuning element 25 is capacitively coupled to the side of the hollow tubular portion 21 within which it is adapted to move, and is floating because of the absence of any direct contact between the element 25 and the resonator walls. It should be noted that the element 25 is a relatively large body and is adapted to provide a relatively large surface area which is very closely spaced from the interior surrounding surface of the tube 21. By controlling the movement of both tuning elements 25, 25 simultaneously, as by means of dial 28, and by arranging one of the elements 25 closer to the central plane through the resonator, I am able to obtain a wider tuning frequency range than known types of cavity resonators which employ bellows or other tuning schemes. If desired, the insu- 3 lators 28. 26 may have threads of l n Ditch so that one tuning element 25 moves farther than t e other with the same movement of dial 28. One advantage of the tuning arrangement of the Present invention is that it eliminates the use of sliding conductors.

The equivalent electrical circuit for the system 01 1 is a regenerative Hartley three-point oscillator circuit, wherein the grid is connected to one end of the tank or oscillatory circuit, the anode connected to the other end of the tank, while the cathode is connected to a point intermediate the ends of the tank.

Fig. 2 is a modification of the circuit of Fig. l and differs therefrom mainly in the manner of feeding the filaments of the vacuum tubes. The

same elements of Figs. 1 and 2 are represented bythe length of the communication wave. The filaments are connected to plates 35 and 36 mounted on opposite sides of and insulated from the oathode floating plate 31. Plates 35 and 36 are bypassed to the cathode plate 31 for energy of the operating frequency and are connected to separate filament heating leads which extend through the interior of the tubular conductor 30. 'I'he cathode plate 31 is directly connected to the free end of the tubular conductor 30 so that the floating cathode plate 31 is at a point of high impedance. Quarter wavelength conductive tube 30 is surrounded by a metallic tubular conductor 3| and connected thereto at one end by means of a metallic end plate 32. Elements 3|), 3| and 32 thus form in effect a concentric line resonator. In view of the particular length chosen for the conductor 30, the free end of this conductor which is connected to the floating cathode plate 31 will be a point of high impedance. The cathode plate 31, because it is floating, will assume the p'oten tial of the gradient in the interior of the resonator by virtue of its location. The grids and anodes of the vacuum tubes I3, I3 are connected to opposite sides of the resonance cavity for radio frequency energy in the same manner as the va uum tubes of Fig. 1.

In one embodiment tried out in practice. the electrical resonator of th present invention employed eighteen RCA-955 Acorn vacuum tubes mounted in a circle within the resonance cavity. and there was obtained an output of three watts at a wavelength of 1.2 meters. The number of tubes mentioned herein, as well as the particular wavelength obtained in the experimental set-up. are given for purposes of illustration only, since obviously more or fewer tubes can be employed, and a longer or a smaller wavelength can be obtained, depending upon the dimensions of the resonance cavity.

What is claimed is:

l. A resonator comprising a hollow chamber of electrically conductive material, a metallic tubular member electrically closed at one end and having an opening in the center of said chamber at a location where the voltage is a maximum, and a tuning element adapted to move within said metallic tubular member and extending within the resonance cavity of said chamber for varying the spacing between two opposite walls of said chamber, said tuning ele- 4 ment having a large sin-face area adjacent to and being capacitively coupled to the sides of the tubular member within which it moves. and means for varying the position of said tuning element with a consequent variation of the resonant frequency of said resonator.

2. A resonator comprising a ,hollow chamber of electrically conductive material, a metallic tubular member electrically closed at one end and having an opening in the center of said chamber at a location where the voltage is a maximum, and a tuning element adapted to move within said metallic tubular member and extending within the resonance cavity of said chamber for varying the spacing between two opposite walls of said chamber, said tuning element having a. large surface area adjacent to and being capacitively coupled to the sides of the tubular member within which it moves, and an insulator rod affixed to one end of said tuning element and extending through the closed end of said tubular member for varying the position of said tuning element.

3. A resonator comprising a hollow chamber of electrically conductive material, a metallic tubular member electrically closed at one end and having an opening in the center of said chamber at a location where the voltage is a maximum, and a tuning element adapted to move within said metallic tubular member and extending within the resonance cavity of said chamber, said tuning element being capacitively coupled to the sides of said tubular member, a similarly arranged tubular member and tuning element oppositely disposed from said first tubular member and tuning element, and means for varying the position of each tuning element.

4. A resonator comprising a hollow chamber of electrically conductive material, a metallic tubular member electrically closed at one end and having an openin in the center of said chamber at a location .where the voltage is a maximum, and a tuning element adapted to move within said metallic tubular member and extending within the resonance cavity of said chamber, said tuning element having a large surface area adjacent to and being capacitively coupled to the sides of the tubular member within which it moves. a similarly arranged tubular element oppositely disposed from said first tubular member and tuning element, and means for simultaneously varying the positions of both tuning elements with a consequent variation of the spacing between tuning elements.

5. A resonator comprising a hollow'chamber of electrically conductive material, a metallic tubular member having an electrically closed end and an open end. said open end terminating at and communicating with the interior of said chamber at a location where the voltage is substantially a maximum. and a. tuning element adapted to move within but insulated from said metallic tubular member and extending within the resonance cavity of said chamber for varying the spacing between two opposite walls of said chamber, said tuning element being capacitively coupled to the sides of the tubular member within which it moves, and means for varying'the position of said tuning element with a consequent variation of the resonant frequency of said resonator.

6. A resonator comprising a hollow chamber of electrically conductive material, a metallic tubular member having an electrically closed end and an open end, said open end terminating at and communicating with the interior of said chamber, and a tuning element adapted to move within said tubular member and extending within the resonance cavity of said chamber for varying the spacing between two opposite walls of said chamber, said tuning element having a large surface area adjacent to and being capacitively coupled to the sides of the tubular member within which it moves. and means for varying the position of said timin element with a consequent variation of the resonant frequency of said resonator.

'7. A resonator in accordance with claim 5, characterized in this that said resonator is in the form of a cylinder with circular end surfaces.

8. A resonator comprising a hollow chamber of electrically conductive material, a metallic tubular member electrically closed at one end and having an opening in the center of said chamber at a location where the voltage is a maximum, and a tuning element adapted to move within said metallic tubular member and extending within the resonance cavity of said chamber for varying the spacing between two opposite walls of said chamber, said tuning element having a large surface area adjacent to and being capacitively coupled to and closely spaced from the sides of the tubular member within which it moves, and means for varying the position of said tuning element with a consequent variation of the resonant frequency of said resonator.

9. A resonator comprising a hollow chamber of electrically conductive material, a metallic tubular member electrically closed at one end and having an opening in the center of said chamber at a location where the voltage is a maximum, and a tuning element adapted to move within said metallic tubular member and extending within the resonance cavity of said chamber, said tuning element being capacitively coupled to the sides of said tubular member, a similarly arranged tubular member and tuning clement oppositely disposed from said first tubular member and tuning element, a threaded insulating rod mounted on each metallic tubular member for supporting its respective enclosed tuning element, whereby there is lacking any direct metallic contact between each timing element and its surrounding tubular member, and

unicontrol means simultaneously adjusting the effective lengthsof both threaded insulating rods.

10. A resonator comprising a hollow chamber of electrically conductive material, a. metallic tubular member electrically closed at one end and having an opening in the center of said chamber at a location where the voltage is a maximum, and a tuning element adapted to move within said metallic tubular member and extending within the resonance cavity of said chamber said tuning element being capacitively coupled to the sides of said tubular member, a similarly arranged tubular member and tuning element oppositely disposed from said first tubular member and tuning element, a threaded insulating rod mounted on each metallic tubular member for supporting its respective enclosed tuning element. whereby there is lacking any direct metallic contact between each tuning element and its surrounding tubular member, said insulating rods having threads of diiierent pitch, and unicontrol means for simultaneously adjusting the effective lengths of both threaded insulating rods.

11. The combination with a resonator comprising a hollow chamber of electrically conductive material, a metallic tubular member electrically closed at one end and having an opening in the center of said chamber at a location where the voltage is a maximum, and a tuning element adapted to move within said metallic tubular member and extending within the resonance cavity of said chamber for varying the spacin between two opposite walls of said chamber, said tuning element having a large surface area adjacent to and being capacitively coupled to the sides of the tubular member within which it moves, and means for varying the position of said tuning element with a consequent variation of the resonant frequency of said resonator, of a vacuum tube located within the interior of said hollow chamber, said vacuum tube having grid and anode electrodes connected to metallic plates mounted on opposite sides of said chamber, said vacuum tube having a filament coupled by a pair of leads to a source of heating supply, said last pair of leads being surrounded by a metallic conductor for adistance measured from the filament which is approximately an odd multiple of a quarter wave, including unity, at the operating frequency, as a result of which the filament is at a point of high impedance.

12. The combination with a resonator comprising a. hollow chamber of electrically conductive material, a metallic tubular member having an electrically closed end and an open end, said open end terminating at and communicating with the interior of said chamber, and a tuning element adapted to move within said tubular member and extending within the resonance cavity of said chamber for varying the spacing between two opposite walls of said chamber, said tunin element having a large surface area adjacent to and being capacitively coupled to the sides of the tubular member within which it moves. and means for varying the position of said tuning element with a consequent variation of the resonant frequency of said resonator, of a plurality of vacuum tubes located within the interior of said chamber, said vacuum tubes having grid electrodes connected to a metallic plate mounted on one side of said chamber, said vacuum tubes having anode electrodes connected to a metallic plate mounted on the opposite side of said chamber, means capacitively coupling said plates to said walls, and means for supporting said vacuum tubes within said chamber.

NILS E. LINDENBLAD. 

